1. Field of the Invention
This invention relates to wiring of semiconductor elements.
2. Description of the Prior Art
Heretofore, Al, W, Ta, Ti, their silicides, aluminum alloy (Al--Si--Cu),etc., copper, copper alloy, polysilicon doped with impurities, etc. have been used for wiring of semiconductors. However, when aluminum is used, there is a problem that heat treatment cannot be performed above 450.degree. C. after forming with aluminum, because aluminum malts at temperatures above 450.degree. C. Polysilicon having a high melting point does not pose such a problem. However, since polysilicon has a high resistance, it is unsuitable for wirings of a long distance or with fine wires.
Alternatively when aluminum is formed on the silicon layer, aluminum enters (spikes) into silicon and may cause breakage of wires. In order to overcome such problems, a conventional method has been to form a thin layer of TiN as a barrier layer on the silicon layer over which aluminum layer is formed. The TiN barrier layer prevents diffusion (spiking) of silicon into aluminum.
However, when the TiN barrier layer is formed and then heat-treated in an atmosphere containing O.sub.2, a possible problem is that Ti is oxidized to form nonconductive titanium oxide so that contacts cannot be made. Another problem is that since TiN is very hard, it may separate from metals or silicon because of difference in coefficients of thermal expansion.